Jesus, Shelvey wasn't the first player to make contact with the ball for one thing, Evans is, secondly Shelvey is off the ground, has all his momentum moving forward and catches Evans ON HIS STANDING LEG, on the front of that leg with that leg having no where to go to cushion the blow. Catch someone with their leg in the air, its rare it will break, it will usually spin a player around though it is possible. Kick a standing leg in the back of the leg, it will usually bend, it has somewhere to give way. Catch someone in a standing leg with studs in the ground from the front. Leg can't bend, leg can't spin away.. its the single most dangerous contact that happens from most tackles.
RVP was clear as day ON THE FLOOR, his left leg, hip, back/side/arm are all ON THE FLOOR, miles before he GETS THE BALL, and he doesn't catch the other player in a dangerous way at all.
What decides who was the injured party in the Shelvey vs Evans case, it would be the studs into the standing leg that could easily have broken Evans leg and clearly hurt, while Shelvey got up uninjured... I would say that pretty much chose who the injured party was.